Tiwa Pakoktom, Masatoshi Aoki, Poonpipope Kasemsap, Samakkee Boonyawat and Pedram Attarod
Release Date: March 14, 2009

CO2 and H2O Fluxes Ratio in Paddy Fields of Thailand and Japan
Tiwa Pakoktom1), Masatoshi Aoki1), Poonpipope Kasemsap2), Samakkee Boonyawat3) and Pedram Attarod4)

1) The United Graduate School of Agricultural Science, Tokyo University of Agriculture and Technology
2) Faculty of Agriculture, Kasetsart University
3) Faculty of Forestry, Kasetsart University
4) Faculty of Natural Resources, University of Tehran

(Received: September 24, 2008)
(Accepted for publication: February 13, 2009)

Abstract:
Measurements of CO2 flux (FCO2) and H2O flux (FH2O) were carried out on paddy fields of Thailand and Japan during the 2004, 2005 and 2006 growing seasons using the Bowen ratio technique. The objective was to determine the water resource requirement to achieve a certain amount of CO2 assimilation per land area and analyze the ratio between FCO2 and FH2O (CWFR = FCO2/FH2O). The relationship between FCO2 and FH2O was investigated using regression analysis in 4 growing stages. Relatively high correlations (r2 = 0.56-0.96, p < 0.01) between FCO2 and FH2O were found when data were grouped by growing stage. Using daytime average data, there was high correlation (r2 = 0.61-0.94, p < 0.01) between daytime average CWFR (CWFRd) and daytime average vapor pressure deficit (VPDd) in paddy fields of Japan and Thailand for each growing stage. Pooled data from Thailand and Japan showed high correlations (r2 = 0.61-0.94, p < 0.01) between CWFRd and VPDd for each growing stage. The developed regression equation was tested using an independent published dataset, and it was found that the estimation error was only 2.7%. The regression equations will be useful for estimating CWFRd by only VPDd and accordingly for assessing the water resource requirement.

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To cite this article:
Tiwa Pakoktom, Masatoshi Aoki, Poonpipope Kasemsap, Samakkee Boonyawat and Pedram Attarod: “CO2 and H2O Fluxes Ratio in Paddy Fields of Thailand and Japan”, Hydrological Research Letters, Vol. 3, pp.10-13, (2009) .

doi:10.3178/hrl.3.10
JOI JST.JSTAGE/hrl/3.10
Copyright (c) 2009 Japan Society of Hydrology and Water Resources